The star forming rings are narrow, with slices showing very sharp radial
cutoffs in
H emission. This implies
that OB stars remain in the rings for their Main Sequence lifetimes,
which constrains the stellar velocity dispersion of the rings:
*
<
rring
/ OB 45 km s-1.
The weak line emission that is sometimes found in ring galaxy disks
is post-starburst in origin, i.e., arising from aging HII
complexes powered by A-stars.